# Removing fan energy from rated COP

This has been covered in a few posts here before, but I'm not sure the prototype approach or the 90.1 budget system formulas will give me what I'm looking for (representing generic systems with a specific rated COP based on default PDs, fan efficiencies, autosized capacities and airflows)

To calculate COP-nf for a generic system, does the following approach (basically removing calculated fan power from the denominator of the COP) work?

- total power input [BTU/hr.] = capacity / COP
- fan power input [BHP] = cfm x PD / (fan-eff x 6356)
- compressor power input = total power in - fan power in
- COP-nf = capacity / compressor power input

(applying the appropriate conversions)

**EDIT: Thinking a bit more about the DOE Prototype method, I'm realizing I should probably add the fan heat to the cooling capacity (i.e., the numerator) for COP-cooling-nf and subtract it for COP-heating-nf to account for the impact fan heat.**

and, if this is a valid approach, for VRF/multi-split systems, is the supply fan power merely the sum of each connected indoor unit's fan power?

lastly, what about other elements of systems that consume energy, could/should these also be removed from the COP denominator? Including those that are defined within the object where COP-nf is an input, such as:

for various coil types

- Crankcase Heater Capacity
- Resistive Defrost Heater Capacity

or other objects necessary to define a system (but don't take COP-nf as an input) such as

ZoneHVAC:TerminalUnit:VariableRefrigerantFlow

- Parasitic Electric Energy Use

For some background if someone comes across this post and would like to know about the standard approaches:

DOE Prototype approach:

cop = (eer / 3.413 + R) / (1 - R)

where R is "the ratio of supply fan power to total equipment power at the rating condition." and 0.12 is typically used

and here are the various formulas from 90.1 (12.5.2.c in 2022):

- cop = -0.0076 * seer * seer + 0.3796 * seer
- cop = 1.48E-7 * coph47 * Q+ 1.062 * coph47 (system 6 and 9 heating)
- cop = -0.0296 * hspf * hspf + 0.7134 * hspf
- cop = 7.84E-8 * eer * Q+ 0.338 * eer
- cop = 0.3322 * eer - 0.2145 (system 8 and 10 cooling)
- cop = 1.1329 * cop - 0.214 (system 8 heating)

@mdahlhausen (tagging you as i see your ID associated with the file), it looks like the openstudio-standards file Prototype.utilities.rb has the prototype formula above defined as giving the COP

fans. Am I incorrect in thinking it should be the opposite?withShort answer is yet. @Jeremy has some fixes in to change it for the next release. https://github.com/NREL/openstudio-st...